Spark ignition systems for internal combustion engines



Nov. 4, 1969 N. J. RUSHTON 3,476,097

SPARK IGNITION SYSTEMS FOR INTERNAL COMBUSTION ENGINES Filed Dec. 19, 1967 I NT OR /V BM MIM ATTORNEYS United States Patent US. Cl. 123-448 4 Claims ABSTRACT OF THE DISCLOSURE In a spark ignition system for an internal combustion engine, a transistor or other semi-conductor switches connected in series with the primary winding of the ignition coil, abnormally conducts. When the transistor is turned off, a spark is produced in the usual way. The timing is governed by a contact breaker driven by the engine, but instead of producing a spark by turning the transistor off each time the contact breaker either opens or closes, the circuit is so designed that a spark is produced each time the contact breaker opens and each time the contact breaker closes, so that the circuit is very suitable for engines which operate at high rotational speeds.

This invention relates to spark ingition systems for internal combustion engines.

A system according to the invention comprises in combination an ignition coil for producing sparks at the plugs of an engine in turn, a semi-conductor switch associated with the primary winding of the ignition coil, a spark being produced each time the semi-conductor switch is turned off, a biasing circuit for turning said switch on, a contact breaker which in use is driven by the engine, and means coupling the contact breaker to the semi-conductor switch and biasing circuit whereby the semi-conductor switch will be turned off each time the contact breaker closes and each time the contact breaker opens.

The production of a spark each time the contact breaker opens as well as each time the contact breaker closes enables the system to be used beneficially on an engine having a large number of cylinders.

The accompanying drawing is a circuit diagram illustrating one example of the invention.

Referring to the drawing, there are provided positive and negative supply lines 11, 12 which in use are connected to the battery of a vehicle through the ignition switch. The lines 11, 12 are bridged by a capacitor 13, and in parallel with the capacitor 13 are connected resistor 14 and a contact breaker 15 which is driven by the engine in the usual way. The junction of the resistor 14 and contact breaker 15 is connected to the line 11 through a diode 16 in series with a resistor 17, and is further connected through a capacitor 18 to the base of an n-p-n transistor 19, the base of which is further connected to the line 12 through a diode 21 and a resistor in series. The emitter of the transistor 18 is connected to the base of an n-p-n transistor 19, the base of which is further connected to the line 12 through a diode 12 and a resistor 20 in series. The emitter of the transistor 19 is connected to the line 12, Whilst its collector is connected to the emitter of an n-p-n transistor 22, the collector of which is connected through a resistor 23, to the line 11, and the base of which is connected to the line 11 through a resistor 24, and is further connected through a capacitor 25 to the junction of the resistor 17 and diode 16.

The collector of the transistor 19 is further connected 3,476,097 Patented Nov. 4, 1969 "ice to the base of n-p-n transistor 26, the base of which is further connected to the line 12 through a resistor 27. The emitter of the transistor 26 is connected to the line 12, whilst its collector is connected to the line 11 through a resistor 28 in series with the primary winding 29 of an ignition coil 31, the secondary winding 32 of the ignition coil being connected through a distributor to the spark plugs of the engine in turn. The collector-emitter path of the transistor 26 is bridged by a voltage dependent resistor 33.

In operation, assuming that a spark has just been produced and the circuit is again in a stable state, current flows through resistor 24 to the base of transistor 22, which conducts and so turns the transistor 26 on, so that current flows in the primary winding 29. Assuming that at this instant the contact breaker 15 is closed, current is also flowing through the resistor 14 and the contact breaker 15, but the capacitor 18 is discharged. At the instant when the contact breaker 15 opens, current flows through resistor 14, capacitor 18 and the base-emitter circuit of the transistor 19 to turn the transistor 19 on, so that the base current flowing to the transistor 26 is diverted through the transistor 19. The transistor 26 therefore switches ofi, and the fall in flux in the ignition coil produces a spark. The time constant of the resistor 14 and capacitor 18 is chosen so that the transistor 19 remains conductive for a predetermined period of time, and at the end of this time the transistor 19 turns off, and the current flow to the base of the transistor 26 is restored. At this stage, the capacitor 18 is charged, and current is again flowing in the primary winding 29.

While the contact breaker 15 is open, current also flows through the resistor 17 to charge the capacitor 25. When the contact breaker 15 closes again, the capacitor 18 discharges through the contact breaker 15 and the diode 21. At the same time, the capacitor 25 discharges and then charges in the reverse direction through the resistor 24, the diode 16 and the contact breaker 15. This charging current diverts the current from the base of the transistor 22, which turns off to remove the base current from the transistor 26, so that once again the flux in the ignition coil core falls and a spark is produced. The previous charging of the capacitor 25 through the resistor 17 results in a larger initial current and enables a smaller capacitor 25 to be used than would otherwise be necessary to achieve a given turn off time for transistor 26.

The transistor 22 turns on again after a period of time determined by the resistor 24 and the capacitor 25, and this period is again chosen so that the current can build up again in the winding 29 before the contact breaker 15 opens again.

The capacitor 13 is included to absorb transients, and the voltage-dependent resistor 33 protects the transistor 26. The resistor 20 minimises risk of the circuit operating spurio-usly as a result of contact bounce.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A spark ignition system for an internal combustion engine, comprising the following combination:

(a) first and second supply lines for connection to the vehicle battery, the second line being grounded,

(:b) an ignition coil having a primary winding and a secondary winding, the secondary winding producing sparks at the plugs of the engine in turn when current flow in the primary Winding is interrupted,

(c) a first transistor having its collector-emitter path in series with the primary winding between the supply lines,

(d) a second transistor having its collector-emitter path in series with the base-emitter path of the first transistor between the supply lines, whereby current can flow through the second transistor to turn the first transistor on,

(e) means coupling the base of said second transistor to a supply line so as to bias said second transistor to conduction,

(f) a third transistor having its collector-emitter path connected across the base-emitter path of the first transistor, whereby said third transistor when conductive removes base current from said first transistor to turn said first transistor otf,

(g) a series circuit across the supply lines incorporating a resistor and an engine driven interrupter, with one terminal of the engine driven interrupter grounded,

(h) a capacitor coupling the junction of the resistor and interrupter to the base of the second transistor, said capacitor charging through said resistor when the interrupter opens to turn on the second transistor and so turn 01f the first transistor and produce a spark, said capacitor being charged before the interrupter opens again, and the second and first transistors turning off and on respectively when the capacitor is charged,

(i) means operable upon closing of the interrupter for discharging the capacitor and removing the bias from the third transistor so that the first transistor is again turned off to produce a spark, said means restoring the bias to the third transistor before the interrupter opens again.

2. A system as claimed in claim 1 in which the means specified at (i) includes a second capacitor coupled to the junction of the resistor and interrupter through a diode, and further coupled to the base of the third transistor, said second capacitor being charged through the interrupter, the diode and the biasing circuit of the third transistor when the interrupter is closed to hold said third transistor off for the required period of time.

3. A system as claimed in claim 2 including a resistor coupling the second capacitor to a supply line to charge the second capacitor while the interrupter is open, whereby when the interrupter closes said second capacitor must first discharge before it charges through the interrupter.

4. A spark ignition system for an internal combustion engine, comprising in combination first and second supply lines for connection to the vehicle battery, the second line being grounded, an ignition coil having a primary winding and a secondary winding, the secondary winding producing sparks at the plugs of the engine in turn when current flow in the primary winding is interrupted, a transistor having its collector-emitter path in series with the primary winding between the supply lines, a biasing circuit providing base current to said transistor from the supply lines to turn said transistor on, a resistor and an engine-driven interrupter connected in series between the supply lines with one terminal of said interrupter grounded, said resistor and interrupter having a junction the potential at which varies between first and second levels as the interrupter opens and closes, and control means sensitive to the potential at said junction, said control means being operative when said potential has one level to turn said transistor oil? by short-circuiting its base current, and being further operative when said potential has its other level to turn said transistor off by interrupting its base current, said control means acting only during a portion of the period of time for which the potential at said junction is at a given level, whereby said biasing circuit always restores current flow in the transistor before the level of potential at said junction changes.

References Cited UNITED STATES PATENTS 3,242,916 3/1966 Coutal. 3,260,251 7/1966 Lange.

LAURENCE M. GOODRIDGE, Primary Examiner US. Cl. X.R. 315-209 

